1. Field of the Invention
This invention pertains generally to neurological diagnostic techniques, and more particularly to an apparatus for performing self-diagnostic measurements of nerve sensory latency such as may be exhibited as a result of carpal tunnel syndrome.
2. Description of the Background Art
Median nerve compression in the wrist, also called “carpal tunnel syndrome” is becoming an increasingly common disorder that causes pain and suffering, as well as a substantial economic impact. Carpal tunnel syndrome has various causes and predispositions which include genetic, toxic, metabolic and traumatic factors. The leading causes of the disorder stem from cumulative trauma or repetitive motion mechanisms. Primarily, the causative factors are related to the nature of the work performed and the ergonomic environment of the workplace.
Carpal tunnel syndrome has become an agonizing disorder for many sufferers while a far larger segment of the population experiences various levels of discomfort and disability. Concomitant economic costs exist which are more easily quantified as costs for medical treatment, disability payments, insurance premiums, along with the economic impact of decreased worker and industrial productivity.
The current medical industry consensus is that measuring the time required for a sensory nerve action to cross the wrist after the occurrence of a depolarizing incident is the most definitive test available for nerve compression. Since nerve conduction is bi-directional, the stimulus can be applied to a finger and recorded from the nerve above the wrist, or the converse, wherein each method is valid and should provide equivalent results. Measurements on conduction times in healthy individuals which are not experiencing compression of the carpal nerves provide a narrow range of conduction times which are reproducible over extended time periods. A nerve under compression responds with a lower conduction velocity, and thereby a longer conduction period, or latency, between the stimulus and the response. Ranges of normal latency values have become well known with a number of comprehensive case studies to be found in the literature.
Diagnostic testing is currently being performed by professionals, such as neurologists and physiatrists in medical offices, clinics, or in neurophysiology laboratories. Various laboratory and clinical equipment is currently available to allow a medical practitioner to assess patient nerve conduction, however, the expense of purchasing and using these devices has limited their use. The equipment typically being employed by the medical community provides a suite of testing functions and includes a waveform display in addition to a digital readout. A percentage of insurance plans, including Medicare®, require the submission of a waveform graph in order for the test costs to be reimbursed. Presently the fee for performing this test (approximately five hundred dollars per examination) puts the technique out of the range of economic feasibility for many applications.
Due to the cost and limited accessibility of the equipment and practitioners, only a small minority of patients receive the definitive testing, and often by the time the testing is performed, the severity of the nerve compression already warrants surgery. The screening of a larger segment of the population to monitor ongoing sensory nerve conduction of those performing vigorous or repetitive motion activities would be a welcome and valued asset within industry, government, and in the field of ergonomics which endeavors to assess and remediate this major debilitating disorder.
Carpal tunnel syndrome may be caused by a number of factors, of which “occupational neuropathy” is but one of at least twenty five identified causes as described in Baker's Textbook of Clinical Neurology. Other common causes include pregnancy, diabetes, congestive heart failure, arthritis and familial heredity. The screening efforts for carpal tunnel syndrome by professionals and their agents or technicians, has focused on larger organizations with known or suspected risk factors. A large percentage of workers, therefore, are unserved by these screening methods, such as those laboring in small businesses, trades or crafts, services and farms, along with many self-employed workers.
Therefore, a need exists for an inexpensive, easy to operate instrument which provides self-diagnostic screening of nerve latency such as median nerve latency which is exhibited as a result of carpal tunnel syndrome. The present invention satisfies those needs as well as others, and overcomes the deficiencies of previous approaches.